Multi-phasic microphotodetector retinal implant with variable voltage and current capability

ABSTRACT

A visible and infrared light powered retinal implant is disclosed that is implanted into the subretinal space for electrically inducing formed vision in the eye. The retinal implant includes a stacked microphotodetector arrangement having an image sensing pixel layer and a voltage and current gain adjustment layer for providing variable voltage and current gain to the implant so as to obtain better low light implant performance than the prior art, and to compensate for high retinal stimulation thresholds present in some retinal diseases. A first light filter is positioned on one of the microphotodetectors in each of the image sensing pixels of the implant, and a second light filter is positioned on the other of the microphotodetectors in the image sensing pixel of the implant, each of the microphotodetectors of the pixel to respond to a different wavelength of light to produce a sensation of darkness utilizing the first wavelength, and a sensation of light using the second wavelength, and a third light filter is positioned on a portion of the voltage and current gain adjustment layer that is exposed to light, to allow adjustment of the implant voltage and current gain of the device by use of a third wavelength of light.

FIELD OF THE INVENTION

The present invention relates to medical products that are implantedinto the eye that can restore a degree of vision to persons with visionloss caused by certain retinal diseases.

BACKGROUND

A variety of retinal diseases cause vision loss by destruction of theouter retinal vasculature and certain outer and inner retinal layers ofthe eye. The inner retina is also known as the neuroretina. The outerretinal vasculature is comprised of the choroid and choriocapillaris,and the outer retinal layers are comprised of Bruch's membrane andretinal pigment epithelium. The outer portion of the inner retinal layerthat is affected is the photoreceptor layer. Variable sparing of otherinner retinal layers, however, may occur. These spared inner retinallayers include the layers of the outer nuclei, outer plexiform, innernuclei, inner plexiform, amacrine cells, ganglion cells, and the nervefibers. The sparing of these inner retinal layers allows electricalstimulation of one or more of these structures to produce sensations offormed images.

Prior efforts to produce vision by electrically stimulating variousportions of the retina have been reported. One such attempt involved adisk-like device with retinal stimulating electrodes on one side andphotosensors on the other side. The photosensor current was to beamplified by electronics (powered by an external source) within the diskto power the stimulating electrodes. The device was designed toelectrically stimulate the retina's nerve fiber layer via contact uponthis layer from the vitreous cavity. The success of this device isunlikely because it must duplicate the complex frequency modulatedneural signals of a nerve fiber layer which runs in a general radialcourse with overlapping fibers from different portions of the retina.Accordingly, the device would not only have to duplicate a complex andyet to be deciphered neural signal, but would also have to be able toselect appropriate nerve fibers to stimulate that are arranged in anon-retinotopically correct position relative of the incident lightimage.

Another attempt at using an implant to correct vision loss involves adevice consisting of a supporting base onto which a photosensitivematerial, such as selenium, is coated. This device was designed to beinserted through an external sclera incision made at the posterior poleand would rest between the sclera and choroid, or between the choroidand retina. Light would cause an electric potential to develop on thephotosensitive surface producing ions that would then theoreticallymigrate into the retina causing stimulation. However, because thisdevice has no discrete surface structure to restrict the directionalflow of the charges, lateral migration and diffusion of charges wouldoccur thereby preventing an acceptable image resolution capability.Placement of the device between the sclera and choroid would also resultin blockage of discrete ion migration to the photoreceptor and innerretinal layers. This is due to the presence of the choroid,choriocapillaris, Bruch's membrane and the retinal pigment epitheliumlayer, all of which would block passage of these ions. Placement of thedevice between the choroid and retina would still interpose Bruch'smembrane and the retinal pigment epithelium layer in the pathway ofdiscrete ion migration. As the device would be inserted into or throughthe highly vascular choroid of the posterior pole, subchoroidal,intraretinal and intraorbital hemorrhage would likely result along withdisruption of blood flow to the posterior pole.

Another retinal stimulating device, a photovoltaic artificial retinadevice, is disclosed in U.S. Pat. No. 5,024,223. This patent discloses adevice inserted into the potential space within the retina itself. Thisspace, called the subretinal space is located between the outer andinner layers of the retina. The disclosed artificial retina device iscomprised of a plurality of so-called surface electrode microphotodiodes(“SEMCPs”) deposited on a single silicon crystal substrate. SEMCPstransduce light into small electric currents that stimulate overlyingand surrounding inner retinal cells. Due to the solid substrate natureof the SEMCPs, blockage of nutrients from the choroid to the innerretina can occur. Even with fenestrations of various geometries,permeation of oxygen and biological substances is not optimal.

U.S. Pat. No. 5,397,350 discloses another photovoltaic artificial retinadevice. This device is comprised of a plurality of so-called independentsurface electrode microphotodiodes (ISEMCPs) disposed within a liquidvehicle, for placement into the subretinal space of the eye. The openspaces between adjacent ISEMCPs allow nutrients and oxygen to flow fromthe outer retina into the inner retina. ISEMCPs incorporate a capacitivelayer to produce an opposite direction electrical potential to allowbiphasic current stimulation. Such current is beneficial to preventelectrolysis damage to the retina a due to prolonged monophasicstimulation. However, like the SEMCP device, the ISEMCP depends uponlight from the visual environment to power it, and so the ability ofthis device to function in low light environments is limited. The ISEMCPalso does not provide a way to address localized variations in thesensitivity to electrical stimulation of surviving retinal tissue.Accordingly, there is a need for retinal implants that can operateeffectively in low light environments and are capable of compensatingfor variations of retinal sensitivity within an eye.

BRIEF SUMMARY

In order to address the above needs, a retinal implant for electricallyinducing formed vision in an eye, a so-called Variable Gain MultiphasicMicrophotodiode Retinal Implant (VGMMRI) is disclosed capable ofproducing positive or negative polarity stimulation voltages and currentboth of greater amplitude in low light environments than the previousart. The increased voltage and current will be called gain.

According to one aspect of the invention, the retinal implant (alsoreferred to herein as a VGMMRI) includes multiple microphotodetectorpairs arranged in columns on the surface of a silicon chip substrate.Each microphotodetector pair in each column has a firstmicrophotodetector and a second microphotodetector having oppositeorientations to incident light so that a P-portion of the first PINmicrophotodetector and a N-portion of the second NiP microphotodetectorare aligned on a first-end on the surface of a column so that they arefacing incident light. Similarly, the N-portion of the first PiNmicrophotodetector and a P-portion of the second NiP microphotodetectorare aligned on a second-end that is opposite the first-end and directedtowards the substrate. The microphotodetector pairs of each column arealso arranged so that the P-portions and N-portions of both ends of allthe microphotodetector pairs line up along the long axis of the column.A common retina stimulation electrode connects the first-end P- andN-portions of each microphotodetector pair. On the second-end, eachcolumn of microphotodetector pairs has a first contact strip inelectrical contact with the second-end N-portions of allmicrophotodetectors in each column, and a second contact strip that isin electrical contact with the second-end P-portions of allmicrophotodetectors in the column. This same arrangement is repeated forall columns of microphotodetector pairs on the device. Thus, each columnof microphotodetector pairs has two independent common second contactstrips on the second-end extending the length of the column and beyondto the ends of two underlying strip-shaped photodiodes, one connectingall the second-end N-portions of all the overlying PiNmicrophotodetector pairs in the column, and the other connecting all thesecond-end P-portions of all the overlying NIP microphotodetector pairsin the column.

Beneath the column, the second-end N-portion common contact strip of thecolumn is in electrical contact with the P-portion of a first underlyingstrip-shaped PiN photodetector, that extends the length of the columnand then beyond at the ends of the column. The purpose of this firstunderlying strip-shaped PiN photodetector is to provide increasedvoltage and/or current to the PIN microphotodetectors in the overlyingcolumn via the second-end N-portion common contact strip. Similarly, thesecond-end P-portion common contact strip is in electrical contact withthe N-portion of a second underlying strip-shaped NiP photodetector thatextends the length of the column and then beyond at the ends of thecolumn. The purpose of this second strip-shaped NiP photodetector is toprovide increased voltage and/or current to the microphotodetectors inthe overlying column via the second-end P-portion common contact strip.

In one embodiment, three types of light filters, each passing adifferent wavelength portion of visible through infrared light, aredeposited, one each, on the first-end P portion of the PiNmicrophotodetectors, the first-end N portion of the NiPmicrophotodetectors, and the P and N portions of the light exposed endsof the first strip-shaped underlying PiN photodetector and the lightexposed ends of the second strip-second underlying NiP photodetector.

According to a second aspect of the resent invention, a method ofadjusting the stimulation voltage amplitude and polarity, and/or currentof a retinal implant positioned inside the eye is disclosed. The methodincludes the steps of providing a light powered retinal implant, theVGMMRI, having an electrical output that can be adjusted in voltagepolarity, voltage, and current amplitude by varying the intensity ofthree different wavelength portions of visible and infrared illuminatinglight directed onto the retinal implant. The three different wavelengthsare provided from incident light and from a headset device forprojecting different wavelengths into the eye. The headset device ismodified Adaptive Imaging Retinal Stimulation System (AIRES) asdescribed in U.S. Pat. No. 5,595,415, incorporated herein by reference,and modified to produce images and background illumination in threedifferent wavelengths of visible and infrared light.

According to a third aspect of the present invention, a retinal implantis disclosed that is fabricated as separated individual VGMMRImicrotile-like pixels each possessing at least one microphotodetectorpair and one pair of underlying strip photodetectors, such that themicrotile-like pixels are held in a mesh-like lattice. The open spacesbetween the pixels within the lattice allow nutrients and oxygen topermeate between the outer and inner retinal layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified cross-sectional side view of an eye containing aVGMMRI retinal implant in the subretinal space;

FIG. 2 is an enlarged exploded perspective sectional view of a portionof the retina illustrating a perspective sectional view of an embodimentof the VGMMRI in its preferred location in the subretinal space;

FIG. 3 is an incident-light-facing plan view of a VGMMRI according to apreferred embodiment of the present invention;

FIG. 4 is a portion of a perspective, stepped-sectional-view of theVGMMRI taken through sections A—A, and B—B of FIG. 3;

FIG. 4A is a plan view of another preferred embodiment of the VGMMRIwherein each microphotodetector pair with its gain adjustment layer isembedded in a lattice-like mesh and separated in space from eachadjacent microphotodetector pair and its respective gain adjustmentlayer;

FIGS. 5A-5C illustrate the stages of fabrication for one preferredembodiment of the VGMMRI;

FIG. 6 is a generalized schematic diagram of a modified Adaptive ImagingRetinal Stimulation System (AIRES), capable of use with the VGMMRI ofFIGS. 3, 4 and 4A;

FIGS. 7 A-D show a modified PTOS device suitable for use in the AIRESsystem of FIG. 6;

FIG. 8 shows the components of an alternative embodiment of the AIRESsystem of FIG. 6;

FIG. 9 is a perspective view of a retinal implant injector (RII) for usein implanting a retinal implant such as the VGMMRI of FIGS. 3, 4, 4A,and 5A-5C;

FIG. 10 is a perspective view of a syringe retinal implant injector(SRI) assembly comprising the RII of FIG. 9 with a retinal implantinside, an attached cannula, and an attached operator controlled fluidfilled syringe; and

FIG. 11 is a perspective view of an alternative embodiment of the SRI ofFIG. 10.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

As described in further detail below, the present invention relates to aretinal implant that can vary its stimulation voltage polarity and alsoproduce higher stimulation voltages and currents to the retina comparedto retinal implants of the prior art. This higher and adjustablestimulation voltage and current allow for higher voltage and/or currentstimulation thresholds that may be required to stimulate severelydamaged retinal tissue. Although a preferred embodiment of the retinalimplant disclosed below may be used on its own, without the need for anyspecial stimulation apparatus positioned outside of the eye, in anotherembodiment the implant stimulation voltages and currents of the presentinvention are adaptable to the specific needs of a retina by theaddition of regulated amounts of different wavelengths of projectedimages and background illumination light provided by a headset devicethat projects the different wavelengths into the eye. The use of thisheadset also allows the retinal implant to function in low lightconditions.

As illustrated in FIG. 1, a retinal implant (also referred to herein asa variable gain multiphasic microphotodiode retinal implant or VGMMRI)10 is positioned inside the eye 12, in the subretinal space 16, and isoriented to receive incident light 11 arriving through the cornea 13 andlens 14 of the eye 12. As used in this specification, the term lightrefers to visible and/or infrared light.

In FIG. 2, a high magnification perspective sectional view shows theVGMMRI 10 placed in its preferred position in the subretinal space 16.The layers of the retina from inside the eye to the outside in theirrespective positions are: internal limiting membrane 18; nerve fiberlayer 20; ganglion and amacrine cell layer 22; inner plexiform 24; innernuclear layer 26; outer plexiform 28; outer nuclear layer 30; andphotoreceptor layer rod and cone inner and outer segments 32, all ofwhich constitute the inner retina 34. It should be noted that the layersof the outer plexiform 28; outer nuclear layer 30; and photoreceptorlayer rod and cone inner and outer segments 32 constitute the outerportion of the inner retina, but are sometimes referred to as just the“outer retina” in the art, although the meaning is clear to one skilledin the art as described in the above context. The VGGMRI 10 is disposedbetween the inner retina 34 and the outer retina 40 comprised of theretinal pigment epithelium 36 and Bruch'membrane 38. External to theouter retina 40 are the choriocapillaris 42 and choroidal vasculature 80is the sclera 48.

Referring to FIGS. 3 and 4, a preferred embodiment of a VGMMRI is shown.FIG. 3 is a incident-light-facing plan view of the VGMMRI 10 showing atop layer 60 of columns 61 of microphotodetector pairs 62, that arepreferably microphotodiode pairs constructed from an amorphos siliconmaterial and arranged on the surface of a underlying gain layer formedfrom a silicon chip substrate. The term microphotodetector, as usedherein, is defined as any device capable of accepting light energy andconverting it into an electrical signal, and/or current gain to thefirst strip-shaped PiN photodiode 66 that provides increased boltageand/or current gain to the first column 63 of the amorphous PiNmicrophotodetectors of the microphotodetector pairs 62 and a secondstrip-shaped NiP photodiode 68 that provides increase voltage and/orcurrent gain to the second column 64 of the amorphousmicrophotodetectors pairs 62. Each amprphous PiN microphotodetector 63Aand each amorphous NiP microphotodetector 64A of each mircophotodetectorpair 62 has a common retinal stimulating electrode 65.

Beneath each microphotodetector column 61, the N-portion common contactstrip 66A (FIG. 3) of the PiN microphotodetector column 63 is inelectrical contact with the P-portion of a first underlying strip-shapedPiN photodetector 66. Also, the common contact strip 66A extends thelength of the column 61 and then beyond to the ends of the P-portion ofthe first strip-shaped PiN photodiode 66. The purpose of this firstunderlying strip-shaped PiN photodetector 66 is to provide increasedvoltage and/or current gain to the overlying PiN microphotodetectors63A.

Similarly, as best shown in FIG. 4, beneath the amporphous siliconmicrophotodetector column 61, the P-portion common contact strip 68A ofthe amorphous NiP microphotodetector column 64 (FIG. 3) is in electricalcontact with the N-portion of the second underlying strip-shaped NiPphotodetector 68. Also the common contact strip 68A extends the lengthof the column 61 and then beyond to the ends of the N-portion of thesecond strip-shaped NiP photodiode 68. The purpose of this secondunderlying strip-shaped Nip photodetector 68 is to provide increasedvoltage and/or current gain to the overlying amorphous NiPmicrophotodetectors 64A.

Although the VGMMRI 10 is preferably formed in the shape of a disc,other shapes including, but not limited to, rectangles, rings, portionof rings, irregular shapes, and other shapes may be fabricated toaddress the shape of the damaged retina to be stimulated. Also, inanother embodiment of this invention shown in FIG. 4A, each VGMMRI pixel62, each with its small section of underlying strip-shaped gainphotodiodes 66, 68, (FIG. 4) may be fabricated as an individual pixel,physically separated in space from another pixel 62, but then commonlyembedded in a lattice-like mesh 17 with other pixels 62. The purpose ofthis mesh structure is to allow nourishment to flow between the innerand outer retina through the channels of the mesh.

Referring again to FIG. 4, a stepped sectional view taken through aportion of the sections A—A and B—B of FIG. 3 further illustrates apreferred embodiment of the VGMMRI 10. FIG. 4 best shows the uppermicrophotodetector pixel layer 60 for receiving incident light images11, and the voltage and/or current gain adjustment layer 100. Themicrophotodetector pixel layer 60 of the VGMMRI 10 is stacked on top ofthe voltage/current gain adjustment photodiode layer 100 and the twolayers 60, 100 are electrically connected in series. Preferably, themicrophotodetector pixels of the upper layer 60 are formed of anamorphous silicon material and the gain adjustment layer 100 is composedof photodetector strips formed of a crystalline silicon material.Additionally, the gain adjustment layer 100 preferably has a greaterarea than the area of the microphotodetector pixel layer 60 so that aportion of the gain adjustment layer 100 extends out beyond theperimeter of the microphotodetector layer 60. In one preferredembodiment, the upper microphotodetector layer 60 covers approximately80% of the gain adjustment layer 100 and is centered on the gainadjustment layer 100 such that the portion of the gain adjustment layerextending beyond the perimeter of the microphotodetector layer 60 isexposed to incident light. In other embodiments, the gain adjustmentlayer 100 may also have the same area as microphotodetector layer 60; inthis case, incident light 11 of a selected range of wavelengths passthrough microphotodetector layer 60 to reach the lower gain adjustmentlayer 100. This result is achieved by taking advantage of the propertyof amorphous silicon to block certain wavelengths of visible light andpass certain wavelengths of infrared light.

The microphotodetector pixel layer 60 is made up of individual pixels 62preferably constructed of an amorphous PiN 63A and an amorphous NiP 64Amicrophotodetector oriented so that the N portion 80 of each NiPmicrophotodetector 64A is adjacent the P portion 76 of each PiNmicrophotodetector 63A, and the P portion 76A of each NiPmicrophotodetector 64A is adjacent the N portion 80A of each PiNmicrophotodetector 63A. An intrinsic layer 78 is between the P portionsand N portions of each microphotodetector 63A and 64A. The P portions76, 76A, intrinsic layer 78, and N portions 80, 80A, of themicrophotodetectors 63A and 64A are all preferably fabricated fromamorphous silicon (a:Si), but may also be made from other photodetectormaterials well known to one skilled in the art. In another embodiment,the VGMMRI 10 may be fabricated by laminating two membranes ofcrystalline silicon (Silicon) microphotodetectors together to produce asimilar structure to the preferred embodiment of this invention. Thiswould be analogous to a multilayer PC board sandwiched together like apiece of plywood. The laminated membranes of crystalline siliconmicrophotodetectors would require interlayer connections and thinsubstrate 3-D silicon processing.

Both a Si/Silicon and Silicon/Silicon devices have their own advantages.Amorphous silicon can be used to fabricate a very thin device. Also,amorphous silicon and has strong light absorbing capability in thevisible range which can add to the efficiency of photodetector devicesmade with this material. Crystalline silicon, however, possesses moredesirable electrical leakage qualities than amorphous silicon that mayprove advantageous in higher operating voltage implementations of amicrophotodetector. This latter fact, however, is more of an issue withhigher operating voltages than in self-biased operation. A laminatedcrystalline silicon structure can also produce very smooth pixelstructures.

Referring again to FIG. 4, beginning with the point incident light 11first reaches the surface of the VGMMRI, the specific structure of onepreferred embodiment will be described. Layer 77 is a lattice-like lightblock fabricated from an opaque material, preferably a suitablethickness of platinum, that prevents cross-talk between pixels 62 ofmicrophotodetector pairs. Each pixel 62 has electrode metallization 65that connects adjacent PiN 63A and NiP 64A microphotodetectors. Theformed inner electrode 81 electrically connects the P-side 76 of the PiNmicrophotodetector 63A with the adjacent N-side 80 of the NiPmicrophotodetector 64A. All PiN microphotodetectors 63A within the samecolumn of pixels of FIG. 3, share a common lower electrode strip 150.Likewise all NiP photodetectors 64A within the same column of pixels 64of FIG. 3, share a common lower electrode strip 83.

Continuing with FIG. 4, the upper electrode 65 has a first upper layer86 of sputtered iridium/iridium oxide deposited on second upper layer 88of platinum. The second upper layer 88 is deposited on a first innerlayer 170 of platinum formed over a second inner layer 92 of titanium.The first inner platinum layer 170 is very thin and is semitransparentto light. It is deposited over another very thin second inner layer ofsemitransparent titanium 92 that forms a silicon adhesion layer toprevent titanium oxidation and to ensure proper surface conductivity.The second upper layer of platinum 88 is thicker and serves as thebuildup metal for the final retinal stimulation electrode 65 completedby deposition of an iridium/iridium oxide layer 86 over the platinumlayer 88. The formed inner electrodes 81; of microphotodetector pairs 62are separated from each other by an insulating cap of silicon dioxide 82having an opening for the retinal stimulation electrode 65.

The semitransparent titanium second inner layer 92 preferably contactsalmost all of the surfaces of the adjacent P portion 76 and N portion 80areas of the microphotodetectors 63A, 64A. It is noted that a metalcontact surface is preferred that contacts as much of the active areasof each microphotodetector as possible to extract proper electricalcurrent. This is because electron mobility can be limited in amorphoussilicon and photon generated electrons in the depletion region may nottravel far in the amorphous silicon material.

The PiN microphotodetector 63A in each microphotodetector pixel 62includes, preferably, a visible-light pass filter 74 designed to allow aportion of visible light spectrum to pass through to excite thePiN-oriented microphotodetector 63A while blocking other wavelengths,including infrared light. In other embodiments, a light pass filter forother wavelengths of visible or infrared light would also be suitable.The NiP microphotodetector 64A of each microphotodetector pixel 62includes preferably an infrared-light pass filter (IR-A) 75 to permit aportion of the infrared light spectrum to pass through to excite the NiPoriented microphotodetector 64A while blocking visible light. A suitablematerial for the IR-A pass filter 75 and the visible light pass filter74 is an interference type filter material, although other filter types,well known to one skilled in the art, would also be suitable.

Although the embodiment of FIGS. 3 and 4 illustrate a microphotodetectorpixel layer 60 with pixels 62 made up of paired PiN 63A and NiP 64Amicrophotodetectors having a particular structure, other types ofmulti-phasic microphotodetector retinal implant (MMRI) structures may beutilized. A detailed discussion of the various MMRI structures adaptablefor use in the microphotodetector pixel layer 60 is presented in ourU.S. Pat. No. 6,230,057 filed Mar. 26, 1998 and our U.S. Pat. No.5,895,415 filed Jun. 6, 1995. The entire disclosure of each of theseapplications is incorporated herein by reference.

In the embodiment of FIGS. 3 and 4, the gain adjustment layer 100 hasalternating columns of PiN 66 and NiP 68 voltage/current gainphotodetector strips. Each PiN 66 and NIP 68 photodetector strip ispreferably a single crystalline photodetector that spans the cord of theVGMMRI 10 at its particular position. A portion of all PiN photodetectorstrips 66 is in electrical contact with the common platinum electrodestrips 150 of the PiN columns of the amorphous microphotodetector pixellayer 60 via a titanium adhesion layer 160. Likewise, a portion of allNiP photodetector strips 68 are in electrical contact with the commonplatinum electrode strips 83 of the amorphous microphotodetector pixellayer 60 via a titanium adhesion layer 98.

In the embodiment shown in FIG. 4, a crystalline silicon substrate 200,which is an N properties substrate, is preferably the starting materialof gain layer 100. The substrate 200 is fabricated on the top side(amorphous silicon side) with alternating P-doped (P+) strips 154 andN-doped (N+) strips 155. Similarly, the bottom side of gain layer 100 isprocessed with alternating N-doped (N+) strips 152 and P-doped (P+)strips 153, where N+ diffusion 152 is physically aligned with the P+diffusion 154, and the P+ diffusion 153 is physically aligned with theN+ diffusion 155. Adjacent photodiode strips of PiN 66 and NiP 68structures are isolated by N+ isolation channel 151 that penetrates thegain layer 100 from both sides, preferably merging in the middle of gainlayer 100. Alternatively, trench isolation, which is well known to oneskilled in the art, can also be used to isolate the photodiode strips66, 68. The strips 66, 68 are aligned in parallel, in an alternatingpattern, with the common electrode strips 150, 83 of the amorphoussilicon microphotodetector layer 60. Each PiN crystalline siliconphotodetector strip 66 is lined up with a respective column of PiNamorphous silicon microphotodetector pixel elements 63A above the commonelectrode strip 150, and each NiP crystalline silicon photodetectorstrip 68 is lined up with a respective column of NiP amorphous siliconpixel elements 64A above the common electrode strip 83. This matchingalignment creates a desired series electrical connection of amorphoussilicon pixels 63A, 64A with their respective silicon photodetectors 66,68 in the gain adjustment layer 100.

The portions of the PiN and NiP strips 66, 68 extending past theperimeter edge of the microphotodetectors 62 are coated with aninfrared-light pass filter (IR-B) 106. The IR-B filter 106 is preferablydesigned to pass a different bandwidth of infrared light than the IR-Afilter 75 on the NiP microphotodetectors 64A of the amorphous siliconmicrophotodetector pixel layer 60. A bottom-side electrode 114, on thebottom side of the VGMMRI 10, preferably covers the entire bottomportion of the gain adjustment layer 100. The bottom-side electrode 114,which is preferably made of an iridium/iridium oxide coating 118deposited over a titanium layer 116, extends over the entire bottom sideof the VGMMRI 10 to allow even current distribution across the “ground”plane of the VGMMRI device 10. The bottom-side titanium layer 116directly contacts all the P+ layers 153 and N+ layers 152. It is notedthat the upper and lower electrodes 65, 114 of the VGMMRI 10 preferablyutilize a titanium layer 88, 116 to maintain proper adhesion andelectrical continuity between the silicon (amorphous or crystalline) andthe sputtered iridium/iridium oxide layers 86, 118.

In one preferred embodiment of this invention, the top amorphous siliconmicrophotodetector layer 60 is approximately 4000 angstroms inthickness. The N-amorphous silicon (N+ a-Si:H) 80, 80A and P-amorphoussilicon (P+ a-Si:H) 76, 76A layers are approximately 150 angstromsthick, while the thicker intrinsic-amorphous silicon (undoped a-Si:H)layer 78 in the middle is approximately 3600 angstroms. The thicknessfor the gain adjustment layer 100 is approximately 15 micrometer (μm)and the bottom side titanium layer 116 and iridium/iridium oxide layer118 of the lower electrode 114 adding approximately 150 angstroms and600 angstroms, respectively. One suitable size and configuration foreach amorphous microphotodetector pixel 62 is an 11 μm by 11 μm square.In this configuration, each NiP 64A and PiN 63A segment is preferably5.5 μm by 11 μm. This size and shape of each microphotodetector pixel 62is preferable because the retinal stimulation electrode center-to-centerspacing in the VGMMRI 10 then approaches the resolution pitch of thehuman retina. Because of the lower fill factor in each pixel 62 as thegeometries of the pixel becomes smaller, more light flux is necessary tomaintain a give current flux. The VGMMRI 10, however, can drive acurrent density more evenly through the retina by its ability toincrease voltage and current gain for an entire area or for anindividual pixel. The term fill factor refers to the area of each pixel“filled” by incoming light. The fill factor is proportional to the totalamount of photoactive surface relative to the amount of the photoactivesurface blocked by the stimulating electrode and any other structures.

The VGMMRI implant 10 may be used in an eye to treat an area of outerretina and/or limited inner retina dysfunction. The shape of the implantmay be fabricated to resemble the shape of that area. Shapes such as adisk, an annular disk, a partial annular disk, or irregular shapes areuseful and readily fabricated by one skilled in the art.

As shown in the plan view of FIG. 4A, in another preferred embodiment,the VGMMRI device 10A is fabricated as an array whose pixel blocks 62Aare preferably comprised of 1 to 9 microphotodetector sub-pixels 62, in1×1, 2×2 or 3×3 blocks, that are then plurally secured in an evenpattern in a mesh-like lattice 17. The mesh-like lattice 17 ispreferably made of a flexible biocompatible material such as silicon ofParylene. The embodiment of FIG. 4A shows 1×1 pixel blocks 62A. Theopenings 18 in the mesh-like lattice 17 allow nourishment, nutrients,oxygen, carbon dioxide, and other biological compounds to pass readilybetween the inner retina (neurosensory retina) and the outer retina (retinal pigment epithelium) and are beneficial to the retina. Thismesh-like lattice 17 design thus aids the biocompatibility of the VGMMRIdevice. 10A.

Wafer Processing of VGMMRI Devices

With reference to FIGS. 5A, 5B, and 5C, a VGMMRI is preferablyfabricated using silicon on insulator (SOI) wafers known in the art. Thetop side is processed first, followed by a back etch of the supportportion of the SOI wafer. This etch will automatically stop at the SOIoxide layer interface. Removal of this oxide layer will reveal thebottom side of the silicon membrane ready for further processing. Thesuitable thickness of the silicon membrane is from approximately 2 to 50microns. Standard ion implantation and diffusion techniques are used toproduce active regions on both sides of the silicon membrane.

FIG. 5A shows a portion of the silicon membrane 200 that is to beprocessed into two VGMMRI pixels with P+ active regions 154, 153 and N+active regions 152, 155 with N+ channel stop regions 151 driven in fromthe top and bottom sides. The active regions on the bottom side have acomplimentary pattern to that of the top side.

FIG. 5B shows continuation of the fabrication process with depositionapproximately 50 angstroms of platinum over 50 angstroms of titanium forthe base metal 66A, 68A, on the top side and patterning this metal layer66A, 68A to form the foundation for the amorphous silicon layer.P+a-Si:H 76A is deposited to a thickness of approximately 150 angstromson the top side and patterned to match the Pt/Ti pattern 68A only overthe N+ regions 155 as shown in FIGS. 5A, 5B. Similarly, approximately150 angstroms of N+a-Si:H 80A is deposited and patterned to match thePt/Ti pattern 66A only over the P+ regions 154 as shown in FIGS. 5A, 5B.A sacrificial 0.1 micrometer thick protective aluminum layer, such as iscommonly used in the art, is used to protect existing features wheneverthis is required in patterning.

Approximately 3700 angstroms of undoped a-Si:H 78 is then deposited overall features. This layer will become the intrinsic layer of the PiN andNiP microphotodiodes in the amorphous silicon side of the finishedVGMMRI device. Continuing with FIG. 5B, approximately 100 angstroms ofN+a-Si:H 80 is now deposited and patterned only over P+a-Si:H areas 76A.Similarly, approximately 100 angstroms of P+a-Si: H 76 is deposited andpatterned over the N+a-Si:H 80A areas.

FIG. 5C shows the final stages in the fabrication of the VGMMRI pixels62. The top transparent electrode 81 of each amorphous photodiode pixel62 is fabricated by depositing approximately 50 angstroms of platinumover 50 angstroms of titanium and patterning the electrode 81 to matcheach PiN 63A and NiP 64A amorphous silicon structure of the pixel 62,also shown in FIG. 5B.

Continuing with FIG. 5C, the filters for the amorphous and crystallinePiN and NiP photodiodes are formed next. For clarity, the fabrication offilters over only one of the VGMMRI pixels 62 is described. To form thevisible light pass filter, a protective aluminum mask layer is depositedon the top side and the aluminum is etched away over the PiN amorphoussilicon microphotodiode 63A of FIG. 5C, and visible light passdielectric filter material 74 is deposited and then patterned to remainonly within these openings. The aluminum mask is now etched away and afresh aluminum mask is deposited. In a similar fashion, the IR-A lightpass filter 75 over the NiP amorphous silicon microphotodiode 64A isformed. After completing the visible light and IR-A pass filter layers74, 75, a platinum layer of 0.5 micrometers is deposited and patternedon the amorphous silicon PiN/NiP electrode area to begin the formationof the electrode 65. The electrode 65 is completed by patterning, usingphotoresist lift-off, approximately 150 angstroms of platinum followedby approximately 600 angstroms of iridium/iridium oxide.

Referring again to FIG. 5C, the IR-B light pass dielectric filter layer106 is now deposited and patterned over only the light facing portionsof the crystalline silicon PiN and NiP photodiodes using the samealuminum protective layer process followed by selective etching andremoval as already described.

As further shown in FIG. 5C, an insulation layer of silicon dioxide 116is patterned between the bottom crystalline silicon P portion 153 andthe bottom crystalline silicon N portion 152. Next, approximately 150angstroms of titanium, followed by approximately 600 angstromsiridium/iridium oxide are deposited on the bottom side to form the rearelectrode 118. This bottom electrode 118 of each VGMMRI pixel 62 caneither be electrically isolated or electrically connected to theelectrodes 118 of other VGMMRI pixels 62, in the latter case to form acommon ground electrode plane in another embodiment of the VGMMRIdevice. Finally, in FIG. 5C, a channel 23 is created between the VGMMRIpixels 62 using reactive ion etching that etches entirely through mostto all of the intervening area of crystalline silicon substrate 200,IR-B filter 106, and back electrode 118. In the preferred embodimentwhere most but not all of the intervening crystalline silicon substrate200 area is etched away, silicon bridges remain in some areas betweenthe VGMMRI pixels 62. The VGMMRI pixels 62 are retained in position bythe silicon bridges in this case. In a preferred embodiment where all ofthe intervening silicon area has been etched away, the VGMMRI pixels 62are embedded in a lattice-like, flexible, biocompatible mesh that hasbeen previously described.

Although both crystalline silicon and amorphous silicon is used in apreferred embodiment, amorphous silicon by itself, or crystallinesilicon by itself, may be used to fabricate the VGMMRI device. Inaddition, as shown in FIG. 5C, although the same IR-B filter 106 is usedin a preferred embodiment to cover the PiN and NiP gain photodiodes ofthe crystalline silicon, in other embodiments, different filters, eachpassing a different portion of IR-B light, are used to cover the PiN andNiP gain photodiodes respectively. These other embodiments providegreater control over the amount of voltage and current gain provided bythe gain photodiodes by allowing individual wavelength portions of IR-Blight to control the gain of the PiN or NiP gain photodiode.

Operation of the VGMMRI

As described above, an advantage of the disclosed VGMMRI 10 in FIGS. 3-5is that voltage and current gain of the VGMMRI 10 can be controlled. Inone preferred embodiment, this gain is controllable for the entireimplant 10 and useable by any of the microphotodetector pixels 62. Whenimplanted in the subretinal space of the eye, the VGMMRI 10 receives thelight of images implanted in the subretinal space. Photovoltaicpotentials are generated at each pixel electrode 65 in proportion to theintensity of the incident light. These photovoltaic potentials areretinotopically disturbed in the shape of the incident images andproduce charges at the iridium/iridium oxide electrodes 65 to theoverlying retinal cells and structure 34 is both resistive andcapacitive. Depending upon which of the microphotodetectors 63A, 64A ofa pixel 62 is stimulated more strongly by the wavelengths of incidentlight, the charge developed at the electrode 65 is either positive ornegative. A positive charge causes the contacting overlying cellstructure 30, 32 of FIG. 2, to produce a sensation of darkness throughdepolarization of cell membranes, while a negative charge causes asensation of light through hyperpolarization of cell membranes.

Although other electrode materials may be used, an advantage of thepreferred iridium/iridium oxide electrode of this invention is that itsupports better DC ionic flow into tissue in addition to having a highercapacitive effect than is possible with other electrode materials suchas platinum. This results in lower work function for the VGMMRI 10 andthus the VGMMRI operates with lower electrode potentials. The lowerelectrode potentials result in better low light performance and lessenpotential electrolysis damage to ocular tissues. Secondly, the largercapacitive effect of the preferred iridium/iridium electrode of theVGMMRI, 10 provides a passive charge balance effect to the tissuesduring capacitive discharge of the electrode during the moments whenlight is absent.

In some instances, the amount of light available at the VGMMRI 10 may below, or the electric stimulation threshold of the retina overlying theimplant may be high. In either case, additional voltage and/or currentgain is necessary to stimulate the surviving cell layers and/orstructures. The VGMMRI 10 embodiment of this invention achieves thedesired gain by stacking two layers of microphotodetectors in series toachieve up to twice the voltage swing. The resultant higher voltagedrives a higher current through the tissues.

As shown in FIG. 4 the amorphous microphotodetector pixel layer 60 isstacked onto the crystalline PiN/NiP microphotodetector strips 66A, 68Aof the gain adjustment layer 100. The layers 60, 100 are stacked suchthat the pixels 62 and their respective PiN and NiP contact strips 66A,68A in the gain adjustment layer 100 are connected in series with theunderlying photodetectors 66, 68. Thus, twice the positive or negativevoltage swing may be attainable as compared to the voltage swingattainable with just the single top PiN/NiP microphotodetector layer 60.

The filters 74, 75, 106 on the VGMMRI 10 allow for control of how muchgain is obtained and where that gain is distributed by allowingdifferent wavelengths of light to preferentially stimulate differentmicrophotodetectors under each filter. Preferably, the filters 74, 75and 106 are fabricated so that each of the three filters pass adifferent wavelength, or range of wavelengths of visible and/or infraredlight. In one embodiment, the IR-A and IR-B filters 75, 106 are selectedto pass a portion of wavelengths in the range of 400 nanometers to 2microns. More preferably, the IR-B filters 106 are selected to pass aportion of wavelengths in the range of 800 nanometers to 2 microns andthe IR-A filters 75 are selected to pass a portion of wavelengths in therange of 400 nanometers to 2 microns. The visible light pass filters 74are preferably selected to pass a portion of wavelengths in the range of400 nanometers to 2 microns, and more preferably in the range of 400 to650 nanometers. The different wavelengths of light may enter the eyefrom the environment and/or from another external source such as theheadset discussed below with respect to FIGS. 6 and 7.

For example, because the portions of the PiN and NiP strips 66, 68 ofthe gain adjustment layer 100 extending outside the perimeter of thepixel layer 60 are coated with the IR-B 106 filter, wavelengths thatpass through the IR-B filter are used to selectively provide power tothe gain layer 100 which in turn provides the additional voltage andcurrent gain to the overlying microphotodetector layer 60. Both the PiNmicrophotodetectors 63A and the NiP microphotodetectors 64A may utilizethis reservoir of power from the gain layer 100. The foregoing mechanismallows the microphotodetectors 63A and 64A to generate higher voltagesand current than they would otherwise generate if not for the underlyinggain layer 100.

Because one of the microphotodetectors 63A, 64A is more sensitive tovisible light and the other more sensitive to IR-A light, respectively,light of these two predominant wavelengths will generate sensations oflight and darkness in the overlying retinal layers; a positive potentialat electrode 65 will produce a sensation of darkness, and a negativepotential a sensation of light. This mechanism is described in greaterdetail in U.S. Pat. No. 6,230,057 and in U.S. Pat. No. 5,895,415, thedisclosures of each are incorporated by reference herein.

In a preferred embodiment, as shown in FIGS. 3 and 4, the VGMMRI implant10 has a rectangular microphotodetector pixel top layer 60 centeredoverlying a larger area gain adjustment layer 100 so that approximately80% of the gain adjustment layer 100 is covered by layer 60 and theremaining 20% of layer 100 is exposed to incident light. Although only20% of the gain adjustment layer 100 is exposed in this embodiment,smaller or larger percentages of exposed area may be fabricated in otherembodiments.

In another embodiment, as shown in FIG. 4A, the VGMMRI 10 has a gainadjustment layer integrated into each pixel 62 and both are physicallyseparated in space from other pixels 62. This configuration allowsindividual VGMMRI pixels 62 to be embedded, as shown, within alattice-like mesh 17. The lattice-like mesh 17 is also configurable tohave a common ground electrode for all the pixels 62.

The visible, IR-A, and IR-B light power supply to the VGMMRI 10 isoptionally provided by an external headset system in addition to thevisible, IR-A, and IR-B provided by an external headset system inaddition to the visible, headset system 230, the so-called AIRES-Msystem 230 of FIGS. 6, 7, 8, is a modification of the PTOS headset ofthe Adaptive Imaging Retinal Stimulation System (AIRES) of U.S. Pat. No.5,895,415.

As shown in FIG. 6, the AIRES-M 230 includes component sub-systems of aProjection and Tracking Optical System (PTOS) headset 232, a Neuro-NetComputer (NNC) 234, an Imaging CCD Camera (IMCCD) 236 and an InputStylus Pad (ISP) 238. A Pupil Reflex Tracking CCD (PRTCCD) 242 that hasincorporated an IR-B LED display (IRBLED) 240, and a visible/IR-A LEDdisplay (VISIRALED) 241, are positoned inside the PTOS 232. A VGMMRI 10is shown in the subretinal space of the eye 12. In operation, IR-A andvisible light images form the VISIRALED 241 within the PTOS 232 areoptically projected into the eye 12, when necessary, for example, duringperiods of low ambient lighting. IR-B Illumination from the IRBLED 240is also projected into the eye when necessary to power the voltage andcurrent gain of layer 100 from FIG. 4. Light intensity, duration,wavelength balance, and pulsing frequency of the VISIRALED 241 andIRBLED 240 is controlled by the NNC 234 and modulated by patient inputsvia the interfaced ISP 238. The IMCCD 236, which is mounted on or in thePTOS headset 232, provide the image inputs to the NNC 234 which in turnprograms the visible, IR-A, and IR-B outputs of the VISIRALED 241 andIRBLED 240. A PRTCCD 242 is integrated into the PTOS headset 232 totrack eye movements via changes in the position of the pupillaryPurkinje reflexes. The PRTCCD 242 outputs to the NNC 234 which in turnshifts the position of projected images from the VISIRALED 241 viaelectronic control to follow the eye movements. The PTOS 232 is alsoprogrammable to provide just diffuse IR-B illumination to the VGMMRI 10without projecting visible or IR-A images.

The PTOS 232 is also programmable via the NNC 234 to project patternedIR-B light onto various VGMMRI pixels in the embodiment where the gainadjustment layer 100 is integrated into each of the VGMMRI pixels andthe VGMMRI pixels are separated in space and embedded in a lattice-likemesh.

FIGS. 7A-7D show a glasses-like configuration 232 of the PTOS componentof the AIRES-M system 230 of FIG. 6. As seen in FIG. 7D, although theschematic of the optical system differs somewhat from the generalizedschematic of the PTOS component 232 demonstrated in FIG. 6, the spiritand function of both versions of the devices are the same. FIG. 7A is atop view of the PTOS 232. It shows the headpad 250, the temple pieces252, and the ambient light intensity sensors 254. FIG. 7B is a frontview of the PTOS 232. It shows the external partiallyreflective/transmissive mirror 248, a supporting nose piece 256, ambientlight intensity sensors 254, and the window for the IMCCD camera 236shown in FIG. 6. FIG. 7C is a phantom side view of the PTOS 232. Itshows an internal IR-A and visible light LED display light source 241.Also shown is the partially reflective/transmissive mirror 248, thesupporting nose piece 256, the headpad 250, one of the temple pieces252, and the power supply and signal wire cable 258 leading to the NNC234 of FIG. 6. FIG. 7D shows the VGMMRI 10 disposed in the subretinalspace of the eye 12 with a focused image 246. It also shows the internalvisible light/IR-A LED display light source 241, the PRTCCD 242, theIRBLED 240 and the external partially reflective/transmissive mirror248. FIG. 8 shows the components of the AIRES-M system, consisting ofthe PTOS 232, the portable NNC 234 which may be secured to the patient'sbody, and the ISP 238 input device.

C. Implantation of the VGMMRI into the Eye

As shown in FIG. 9, a retinal implant injector (RII) 300 may be used toplace a retinal implant 302 into the vitreous cavity of the eye, or toplace a retinal implant 302 directly into the subretinal space of theeye. The RII 300 employs a fluid, which is placed inside the RII 300, topush the retinal implant 302 to its exit at the terminal tip 304 of theRII 300. By this means, controlled deposition of the retinal implant 302is possible without physically having to hold the retinal implant 302with an instrument that can cause damage to the implant 302.

Also shown in FIG. 9, the RII 300 is fabricated from tubing which ispreferably made of Teflon (polytetrafluoroethylene) or Parylene and istransparent. It is flattened through most of its length with a taper 304at the tip of its flattened end. The flattened cross-section 306preferably is similar to the cross-section of the retinal implant 302.The opposite end of the tube maintains a round cross-section 308 thatallows the RII 300 to be inserted around a cannula 310 as shown in FIG.10, that in turn is attached to a syringe 312 containing the fluid 314used for the injection. The injection fluid 314 is any biocompatiblefluid but is preferably saline or a viscoelastic material.

As shown in FIG. 10, in use, the retinal implant 302 is first placedwithin the RII 300. The RII 300 is then attached around a cannula 310that in turn is attached to a syringe 312 containing the preferredsaline or viscoelastic fluid. The entire Retinal Injector Assembly 316is held by the operator via the syringe 312. The tapered tip 304 of theRII 300 is then advanced into the vitreous cavity of the eye through anopening made through the eye wall for this purpose. Once the tip 304 ofthe RII 300 is placed into position within the vitreous cavity and nextto the retinotomy incision made through the retina, the retinal implant302 is pushed out of the RII 300 by fluid pressure exerted by operationof the fluid filled syringe 312 from outside the eye. The retinalimplant is then manipulated with surgical instruments either to aposition underneath the retina in the subretinal space, or on top of theretina in the epiretinal position. The RII 300 is also useable todirectly inject the retinal implant 302 through the retinotomy openinginto the subretinal space. In this case, the tip 304 of the RII 300 isplaced directly into the retinotomy opening before injection of theretinal implant 302.

In another embodiment, as shown in FIG. 11, a RII-1 injector assembly416 utilizes an injector plunger 420, placed within the injector 400, topush the implant 402 out of the injector 400. The injector plunger 420is shaped to conform to the inside cross-section of the injector 400 andis attached to any variety of well-known methods of moving the plunger420 forward. In the preferred embodiment, a rod-like extension 425connects the injector plunger 420 to the syringe plunger 435 of asyringe 430. Pushing the syringe plunger 435 thus pushes the injectorplunger 420 forward and moves the implant 402 out of the injector 400.

From the foregoing, a VGMMRI retinal implant having a multilayerstructure of PiN and NiP microphotodiode pairs is disclosed in astructure allowing for voltage and current gain adjustment. In apreferred embodiment, the VGMMRI microphotodetector pixel structure isrectangular, although a round shape or other shapes may be implementedfor the VGMMRI microphotodetector pixel structure, and easily fabricatedby one ordinarily skilled in the art. In another preferred embodiment,the VGMMRI microphotodetector pixels are fabricated as individual unitsseparated in space and embedded in a lattice-like mesh. The mesh mayalso have a common conductor that contacts all the ground electrodes ofthe microphotodetector pixels on the mesh, providing a common groundplane.

It is intended that foregoing detailed description should be regarded asillustrative rather than limiting, and that it be understood that thefollowing claims, including all equivalents are intended to define thescope of this invention.

We claim:
 1. A retinal implant for electrically inducing formed visionin an eye, the retinal implant comprising: a plurality of first layermicrophotodetector pairs for receiving light incident on the eye, eachfirst layer microphotodetector pair comprising: a PiN microphotodetectorand a NiP microphotodetector, wherein the P-portion of the PiNmicrophotodetector and the N-portion of the NiP microphotodetector arealigned on a first end, and the N-portion of the piN microphotodetectorand the P-portion of the NiP microphotodetector are aligned on a secondend; and a common electrode in electrical communication between theP-portion and the N-portion of the first end of the microphotodetectorpair; a gain adjustment layer having a first side and a second side, thefirst side having a first portion electrically connected in series withthe second end of at least a portion of the plurality of first layermicrophotodetector pairs, and a second portion integrally formed withthe first portion and extending away from the first portion, wherein thesecond portion is oriented to receive light incident on the eye; and, acommon electrode plane in electrical contact with the second side of thegain adjustment layer, whereby the common electrode plane serves as anelectrical ground for the retinal implant.
 2. The retinal implant ofclaim 1, wherein the gain adjustment layer comprises at least one PiNphotodetector having a P-portion and an N-portion, the P-portion of theat least one PiN photodetector of the gain adjustment layer inelectrical communication with the N-portion of at least one of the PiNmicrophotodetectors of the first layer microphotodetector pairs.
 3. Theretinal implant of claim 1, wherein the gain adjustment layer comprisesat least one NiP photodetector having a N-portion and a P-portion, theN-portion of the at least one NiP photodetector in electricalcommunication with the P-portion of at least one of the first layer NiPmicrophotodetectors of the first layer microphotodetector pairs.
 4. Theretinal implant of claim 1, wherein the gain adjustment layer comprisesa plurality of parallel PiN and NiP photodetector strips.
 5. The retinalimplant of claim 4, wherein the plurality of first layermicrophotodetector pairs further comprises columns of microphotodetectorpairs, wherein the N-portion of the PiN microphotodetector in a pair isin electrical communication with a P-portion of a PiN photodetectorstrip in the gain layer and the P-portion of the NiP microphotodetectorin the pair is in electrical communication with a N-portion of a NiPphotodetector strip in the gain layer.
 6. The retinal implant of claim4, wherein the plurality of parallel PiN and NiP photodetector stripsare positioned in an alternating pattern.
 7. The retinal implant ofclaim 1, wherein the first end of the second portion of the gainadjustment layer is coated with a first filter material configured topass a first predetermined portion of wavelengths of visible andinfrared light selected from a range of 400 nanometers to 2 microns. 8.The retinal implant of claim 7, wherein the first predetermined portionof wavelengths is selected from a range of 800 nanometers to 2 microns.9. The retinal implant of claim 7, wherein each of the plurality offirst layer microphotodetector pairs further comprises a second filtermaterial positioned over the N-portion on the first end of at least oneof the plurality of microphotodetector pairs.
 10. The retinal implant ofclaim 9, wherein the second filter material is configured to pass asecond predetermined portion of wavelengths of visible or infrared lightin a range of 400 nanometers to 2 microns.
 11. The retinal implant ofclaim 10 wherein the second predetermined portion of wavelengths isdifferent than the first predetermined portion of wavelengths.
 12. Theretinal implant of claim 11 wherein the second predetermined portion ofwavelengths is selected from a range of 650 nanometers to 800nanometers.
 13. The retinal implant according to any of claims 7-11wherein each of the plurality of first layer microphotodetector pairsfurther comprises a third filter material positioned over the P-portionon the first end of at least one of the plurality of microphotodetectorpairs.
 14. The retinal implant of claim 13, wherein the third filtermaterial is configured to pass a third predetermined portion ofwavelengths selected from a range of 400 nanometers to 2 microns. 15.The retinal implant of claim 14 wherein the third predetermined portionof wavelengths is different than the first and second predeterminedportions of wavelengths.
 16. The retinal implant of claim 15, whereinthe third predetermined portion of wavelengths is selected from a rangeof 400 nanometers to 650 nanometers.
 17. A retinal implant forelectrically inducing formed vision in an eye, the retinal implantcomprising: a plurality of microphotodetector pixels, each of theplurality of microphotodetector pixels spaced apart from any adjacentmicrophotodetector pixels and each of the pixels embedded in alattice-like mesh, wherein each of the microphotodetector pixelscomprises: at least one first layer microphotodetector pair forreceiving light incident on the eye, each microphotodetector paircomprising: a PiN microphotodetector and a NiP microphotodetector,wherein the P-portion of the PiN microphotodetector and the N-portion ofthe NiP microphotodetector are aligned on a first end, and the N-portionof the PiN microphotodetector and the P-portion of the NiPmicrophotodetector are aligned on a second end; and a common electrodein electrical communication between the P-portion and the N-portion ofthe first end of the microphotodetector pair; and a gain adjustmentlayer having a first side and a second side, the first side having afirst portion electrically connected in series with the second end of atleast a portion of the plurality of first layer microphotodetectorpairs, and a second portion integrally formed with the first portion andextending away from the first portion, wherein the second portion isoriented to receive light incident on the eye.
 18. The retinal implantof claim 17 wherein the lattice-like mesh comprises a common groundelectrode electrically connected to all of the plurality ofmicrophotodetector pixels.
 19. A retinal implant for electricallyinducing formed vision in an eye, the retinal implant comprising: afirst layer comprising a plurality of microphotodetector pairs, eachmicrophotodetector pair comprising: a PiN microphotodetector and a NiPmicrophotodetector, wherein the P-portion of the PiN microphotodetectorand the N-portion of the NiP microphotodetector are aligned on a firstend, and the N-portion of the PiN microphotodetector and the P-portionof the NiP microphotodetector are aligned on a second end; and a commonelectrode in electrical communication between the P-portion and theN-portion of the first end of the microphotodetector pair; a firstcommon electrode strip in electrical contact with the N-portions of thesecond end of each of the plurality of PiN microphotodetectors of themicrophotodetector pairs; a second common electrode strip in electricalcontact with the P-portions of the second end of each of the pluralityof NiP microphotodetectors of the PiN/NiP microphotodetector pairs; asecond layer photodetector gain adjustment layer comprising a first endand a second end, the first end comprising a first portion electricallyconnected in series with the common electrode strips of both theN-portion and P-portion of the second end of the first layer ofmicrophotodetector pairs, and a second portion integrally formed withthe first portion extending away from the first portion and oriented toreceive light incident on the eye; and a common electrode plane for thesecond layer photodetector gain adjustment layer in direct electricalcontact with the second end of both the first portion and the secondportion of the photodetector, gain adjustment layer, the commonelectrode plane serving as the electrical ground of the retinal implant.20. An adjustable voltage and current gain microphotodetector retinalimplant for electrically inducing formed vision in an eye, the retinalimplant comprising: a first microphotodetector layer comprising at leastone PiN microphotodetector, the first microphotodetector layer having abandpass filter configured to pass visible light, and a voltage andcurrent gain adjustment layer comprising at least one PiN photodetector,the voltage and current gain adjustment layer having a first sidecomprising a first portion electrically connected in series with, andcovered by, a portion of the at least one PiN microphotodetector of thefirst microphotodetector layer, and a second portion, not covered by thefirst microphotodetector layer, comprising an infrared bandpass filter.21. The retinal implant of claim 20, further comprising at least oneupper electrode positioned on the first microphotodetector layer, and atleast one lower electrode positioned on the voltage and current gainadjustment layer, the upper and lower electrodes comprising sputterediridium/iridium oxide.
 22. An adjustable voltage and current gainmicrophotodetector retinal implant for electrically inducing formedvision in an eye, the retinal implant comprising: a firstmicrophotodetector layer comprising at least one PiN microphotodetector,the first microphotodetector layer comprising an amorphous siliconmaterial, wherein the first microphotodetector layer is oriented toreceive light incident on the eye; and a gain adjustment layercomprising at least on PiN photodetector, the PiN photodetector having afirst side electrically connected in series with, and covered by, the atleast one PiN microphotodetector of the first microphotodetector layer.23. The retinal implant of claim 22, wherein the firstmicrophotodetector layer is configured to pass a portion of the lightincident on the eye and the first side of the at least one PiNphotodetector of the gain adjustment layer receives the portion of lightthrough the first microphotodetector layer.